Electric discharge tube



1959 G. o. CROWTHER ET AL 2,900,551

ELECTRIC DISCHARGE TUBE Filed Dec. 20, 1955 OWTH ER TOSSWILL INVENTOR GERALD OFFLEY CR CHRISTOPHER HALY ELECTRIC DISCHARGE TUBE Gerald Oilley Crowther, New Malden, and Christopher Haly Tosswill, Reigate, England, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Application December 20, 1955, Serial No. 554,343

Claims priority, application Great Britain December 21, 1954 3 Claims. (Cl. 313-193) This invention relates to glow discharge tubes comprising a cold cathode and a perforated screen between the anode and the cathode.

The maximum frequency of operation in a glow discharge tube is to a substantial degree dependent upon the time taken to de-ionise the gas. More particularly, if the discharge has existed only a very short time till the moment of extinction, the de-ionisation time is substantially determined by the ion cloud, which exists near the anode and must travel to the cathode.

The object of the invention is to provide a tube having a short de-ionisation time.

According to the invention, in a cold cathode glow discharge tube, in which a perforated screen is arranged between the anode and the cathode, the anode and the cathode are so positioned with respect to the aperture of the screen that the discharge path passes from the cathode through the aperture in thescreen and then bends towards the anode, which is near the screen and parallel thereto, in such manner that more than half of the discharge path is substantially parallel to the screen, the breakdown voltage between the anode and the cathode via the aperture in the screen being lower than by any other path and the breakdown and burning voltages of the screen to any positive electrode being comparatively high.

With the arrangement according to the invention, it is achieved that a substantial part of the discharge path passes close by along the screen, so that a large number of the positive ions in the discharge and especially those near the anode travel to the screen, at least if it is sufiiciently negative at this moment with respect to the other electrodes. Since the distance to be covered for the majority of ions is then considerably smaller than would be the case in the absence of the screen, the de-ionisation time is considerably reduced.

Preferably, the screen between the anode and the cathode is planar and the discharge bends at a right angle. The aperture in the screen may alternatively be an incision in the edge.

In order that the invention may be readily carried into elfect, it will now be described, by way of example, with reference to the accompanying drawing, in which Fig. l is a cross-sectional view of the electrode assembly of a tube according to the invention.

Figs. 2 and 3 are perspective views of the electrode assembly as viewed from the cathode side and from the anode side, respectively.

Fig. 4 shows a circuit arrangement comprising a tube according to the invention, in which at the instant of extinction the screen between the anode and the cathode is the most negative electrode.

Referring to Figs. 1, 2 and 3, the electrode assembly comprises a cathode 1 in the form of an apertured small plate, an anode 2, a de-ionising screen 3, an ignition anode 4 and an ignition cathode 5, which projects through the cathode and extends close to the screen.

States Patent The screen 3 is of material such that the ignition voltage to any positive electrode is higher than 300 volts and the burning voltage is higher than 150 volts.

In operation a priming discharge between the ignition cathode and the ignition anode is maintained for suppressing ignition delays. A negative voltage pulse on the ignition cathode initiates a discharge between the cathode and the ignition anode, whereupon the main discharge path is ignited, if the voltage between the anode and the cathode is sufficiently high. If care is taken to ensure that at the moment of extinction the screen is the most negative electrode in the tube or as negative as the cathode, the majority of ions actually take the shortest distance to the screen.

In the circuit arrangement of Fig. 4, which itself is the subject of our co-pending patent application Serial No. 554,345, the glow discharge tube 20 comprises a main cathode 21, an ignition cathode 22, an apertured deionising screen 23 and a main anode 25.

The cathode 21 is connected to the negative terminal of a voltage source via the parallel combination of a resistor 26 and a capacitor 27, while the anode 25 is connected to the positive terminal of the voltage source via a resistor 28 and a parallel capacitor 29.

The ignition cathode is connected to the negative terminal of the voltage source via a resistor 30 and connected via a capacitor 31 to a terminal 32, to which negative ignition pulses may be supplied as described, for example, in US. Patent 2,768,330. The ignition anode 24 is connected via a resistor 35 to the positive terminal of the voltage source and connected via a capacitor 36 to the negative terminal. Furthermore, the auxiliary anode 24 is connected via a rectifier 34 to terminal 33, to which a constant voltage V is applied. The rectifier 34 prevents the voltage of the ignition anode 24 from rising above that of terminal 33 during the main discharge.

A potentiometer, comprising resistors 37 and 38, serves to apply voltage to the screen 23, which voltage is preferably substantially equal to that of the equipotential surface, in which the screen lies, or the mean voltage of such surfaces. This voltage is usually about volts.

In the absence of input pulses on the ignition cathode 22, a small constant priming current flows between the ignition anode 24 and the ignition cathode 22, the ignition anode taking up a potential slightly less than the. voltage V The arrival of a negative pulse on the; ignition cathode 22 causes the capacitor 36 to discharge. to the main cathode 21 and thus anode to cathode break down to follow. Due to the parallel combination of resistor and capacitor in both the anode circuit and the cathode circuit, the discharge reduces the potential difference between the anode and the cathode to a considerable extent, till the extinction voltage is reached and the discharge extinguishes automatically.

The values of capacitor 27 and resistor 26 are so chosen that at the instant of ignition the screen 23 is negative with respect to the cathode. This has a favorable efiect upon the de-ionisation because of the higher speed of the ions and the shorter paths to be covered.

Due to the rise in cathode potential, the potential of the ignition anode 24 remains comparatively high, since it is coupled by-the discharge with that of the cathode, but the potential of the ignition anode 24, due to the presence of rectifier 34, can never become higher than the voltage V,,.

The advantages are, however, that after extinction of the discharge, the ignition anode immediately has the proper potential again for initiating a discharge, even when the voltage difierence between anode and cathode is still insufiicient for ignition of a new main discharge. The time constant of the circuit of the ignition cathode is less than that of the main cathode, whereas that 01,:

the ignition anode is higher than that of the main cathode. v

What is claimed is:

1. A glow-discharge'tube comprising a sealed envelope containing an ionizable medium at a pressure at which the tube operates with a glow-discharge and enclosing a cathode electrode, a planar screen electrode spaced from said cathode, said screen electrode having an aperture therein through which an axis intersecting the oathode passes, and an anode positioned in proximity to said screen electrode and on the side thereof remote from the cathode, saidanode being positioned on one side of said axis a distance therefrom at which a discharge path extending between the cathode and anode passes through said aperture and is substantially parallel to said screen electrode, the length of said discharge path from said aperture to said anode being more than onehalf of the length of the discharge path between the anode and cathode, whereby the breakdown potential between the anode and cathode in said discharge path is lower than by any other path, the breakdown and buming potentials of the screen electrode relative to any positive electrode being comparatively high.

2. A glow-discharge tube comprising a sealed envelope containing an ionizable medium at a pressure at which the tube operates with a glow-discharge and enclosing a cathode electrode, a planar screen electrode spaced from said cathode, said screen electrode having an aperture therein through which an axis intersecting the cathode passes, and an anode positioned in proximity to said screen electrode and on the side thereof remote from the cathode, said anode being positioned on one side of said axis a distance therefrom at which a discharge path extending between the cathode and anode passes through said aperture and is substanially perpendicular to said axis and parallel to said screen electrode, the length of said discharge path from said aperture to said anode being more than one-half of the length of the discharge path between the anode and cathode, whereby the breakdown potential between the anode and cathode in said discharge path is lower than by any other path, the breakdown and burning potentials of the screen electrode relative to any positive electrode being comparatively high.

3. A glow-discharge tube comprising a sealed envelope containing an ionizable medium at a pressure at which the tube operates with a glow-discharge and enclosing a cold cathode electrode comprising a flat plate having an aperture therein, a planar screen electrode spaced from said cathode, said screen electrode being spaced from said cathode and having an aperture therein which is axially aligned with the aperture in the cathode electrode, an auxiliary ignition cathode electrode extending through the aperture in said cathode electrode into the space between the cathode electrode and screen electrode, an anode positioned in proximity to said screen electrode and on the side thereof remote from the cathode, said anode being positioned on one side of said axis a distance therefrom at which a discharge path extending between the cathode and anode passes through said aperture and is substantially perpendicular to said axis and parallel to said screen electrode, the length of said discharge path from said aperture to said anode being more than one-half of the length of the discharge path between the anode and cathode, whereby the breakdown potential between the anode and cathode in said discharge path is lower than by any other path, the breakdown and burning potentials of the screen electrode relative to any positive electrode being comparatively high, and an ignition anode spaced from said screen electrode and axially aligned with the apertures in said cathode and screen electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,714,403 Smith May 21, 1929 2,068,287 Gabor Ian. 19, 1937 2,152,992 Francis Apr. 4, 1939 2,514,165 Ramsay July 4, 1950 

